This application claims the priority of Austrian Patent Application Serial No. A 357/2000, filed Mar. 3, 2000, the subject matter of which is incorporated herein by reference.
This application is a continuation of prior filed copending PCT International application no. PCT/AT01/00053, filed on Feb. 21, 2001.
The invention relates to a drill, and in particular to a Forstner bit or multi-spur machine bit, having a drill stem and a cutter head, which has a central mandrel, from which a first end cutting edge and a second end cutting edge extend radially outward in opposite in-feed directions. In each case, the cutting head is delimited at the periphery by one wall, which is in the form of a segment of a hollow cylinder and has a peripheral cutting edge adjoining the peripheralside ends of the first and second end cutting edges. At its end, which is remote from the end cutting edge, the wall delimits a chip space which in each case opens out toward the other end cutting edge and penetrates through the drilling head.
Drills of this type are mass-produced products, which are intended for use in handheld, pillar, dowel or in-line multiple-spindle drilling machines and are produced and sold in large numbers. They can be used to drill holes with a relatively large diameter into a very wide range of materials, from plastic-coated chipboards, glued wooden boards through to acrylic plastic sheets and other base materials. The drawback of drills which have become known hitherto are the relatively high drilling forces or torques which have to be applied by the drilling machines, since the straight edges of the end cutting edges and the peripheral cutting edges have to overcome a high resistance from the material.
Accordingly, the peripheral cutting edges of known drills of this type tend to overheat on account of the high level of load during the drilling operation, which becomes apparent from a blue start-up mark. This leads to permanent damage to the drill. To avoid this overheating effect, peripheral cutting edges with a tooth-like design have been used. However, these lead to a failure of the drill to cut cleanly and to the drilled hole tearing open.
It would therefore be desirable and advantageous to provide an improved drill to obviate prior art shortcomings and to reduce the wearing tendency on the drill.
Accordingly, an object of the present invention to provide an improved drill of the type as described herein obviating the afore-stated drawbacks.
According to one aspect of the present invention, an improved drill of the type as described herein is provided obviating the afore-stated drawbacks. In particular, it is an aspect of the present invention to provide an improved drill with the aid of which it is possible to increase the efficiency of the energy employed for a drilled hole to be made and with which it is possible to carry out drilling operations using low drilling forces, with the material load on the drill being kept at a relatively low level.
These aspects, and others which will become apparent hereinafter, are attained in accordance with the present invention by providing drill, especially a Forstner bit or multi-spur machine bit, which includes a drill stem and a cutter head, which has a central mandrel, from which a first end cutting edge and a second end cutting edge extend radially outward in opposite in-feed directions, in each case one wall, which delimits the periphery of the cutting head, is in the form of a segment of a hollow cylinder and has a peripheral cutting edge, adjoining the peripheral-side ends of the first and second end cutting edges, which wall, at its end which is remote from the end cutting edge, delimits a chip space which in each case opens out toward the other end cutting edge and penetrates through the drilling head, and wherein the two peripheral cutting edges have undulating recesses and elevations at least along part of their profile.
The present invention resolves prior art problems by so configuring the drill that the undulating peripheral cutting edges, which act as taper taps, reduce the constant friction within the drilling material which occurs with known peripheral cutting edges to more or less punctiform friction, thus avoiding permanent rubbing. Consequently, a lower drilling machine torque is required to drill a hole, and consequently the drill penetrates into the wood, for example, considerably more easily.
In a further refinement of the invention, it is possible to provide for the undulating recesses and elevations to be formed by cylindrical grinding.
Forming a cylindrically ground profile on the peripheral cutting edge ensures very clean cutting on the part of the drill and prevents the drilled hole from tearing open.
Furthermore, the invention relates to a process for producing a drill, especially a Forstner drill or a multi-spur machine bit. Accordingly, it is a further aspect of the invention to allow automated machining of the cutting edges of a drill in a technically simple and precise way.
In accordance with the invention, this is achieved by the fact that undulating recesses and elevations are hard-milled into the peripheral cutting edges of the hardened drilling head along its profile.
After the drill bit blank has been hardened, the drill stem is ground, and then the elevations and recesses are hard-milled using a hard-milling machine, in particular so as to form a cylindrically-ground profile. In this way, it is possible to achieve a highly accurate configuration of the peripheral cutting edges.